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Soybean pest rankings differ

Midwestern entomologists disagree over the rankings for soybean’s top five insect pests, which include the following:

Soybean aphids

“Although often very sporadic, soybean aphids are most likely to be of economic importance in the northern Midwest year-in and year-out,” says Gray. “Soybean aphids are primarily a problem for Illinois in very mild growing seasons. Hot and dry summers work against their establishment.”

In Nebraska, soybean aphid populations failed to reach economically critical levels in most parts of the state last year, says Wright, “because of the high temperatures, which suppress aphid growth and reproduction.”

A harsh winter with many freeze-thaw cycles will also decrease soybean aphid populations by reducing egg survival, says Krupke. “We haven’t had any widespread pressure from soybean aphids in Indiana since 2005,” he says.

Japanese beetles

This leaf-chomping insect is rapidly increasing in numbers in Illinois and Iowa. “I would place Japanese beetle at least number two for soybeans,” says Gray.

However, certain weather conditions have the potential to reduce Japanese beetle populations. “The Japanese beetle overwinters as a larva in the soil, so mild conditions may help their survival rate,” says Krupke. “They also tend to emerge sooner after a warmer-than-usual spring.”

Bean leaf beetles

A warm fall and a mild winter will favor increased bean leaf beetle populations, says Krupke. “During the last couple years, bean leaf beetles have definitely been worse than normal late in the year,” he says. “We’ve seen more pod feeding from bean leaf beetles in the last two years than in any of the previous 10 years. That may be partially an indirect result of less spraying for soybean aphids.”

In Nebraska, bean leaf beetles are typically only a periodic problem, says Wright. “Early season populations can be suppressed by using a neonicotinoid seed treatment,” he adds.

Spider mites

Indiana soybeans suffered from large spider mite populations last year because of the drought, says Krupke. Spider mites were also widespread in Illinois, Iowa and Nebraska, for the same reason.

Stink bugs and Dectes stem borer

These two soybean pests have recently become a common problem in Nebraska, reports Wright. The Dectes stem borer is more common in south-central Nebraska. “There are few control options available for them,” he says. “So, we recommend early harvest if they’re abundant.”

Stink bugs are now becoming a potential late-season soybean pest problem due to feeding on seeds within pods, Wright adds.